linux-kernel - Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

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Message-ID: <16fdd37a-b9cc-1045-1497-2cfff6af176a@intel.com>
Date:   Mon, 17 Dec 2018 11:53:28 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        X86 ML <x86@...nel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        linux-sgx@...r.kernel.org, nhorman@...hat.com,
        npmccallum@...hat.com, "Ayoun, Serge" <serge.ayoun@...el.com>,
        shay.katz-zamir@...el.com,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Svahn, Kai" <kai.svahn@...el.com>, mark.shanahan@...el.com,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

On 12/17/18 11:49 AM, Jarkko Sakkinen wrote:
>> Yeah, the code is built to have one VMA and only one VMA per enclave.
>> You need to go over the origin of this restriction and what enforces this.
> It is before ECREATE but after that you can split it with mprotect().
> 
> Lets take an example. I'm not sure how we would acquire mm efficiently
> in sgx_encl_page_reclaim() otherwise than having it as a field in encl.

You're effectively rebuilding reverse-mapping infrastructure here.  It's
a frequent thing for the core VM to need to go from 'struct page' back
to the page tables mapping it.  For that we go (logically)
page->{anon_vma,mapping}->vma->vm_mm->pagetable.

This, on the other hand, is trying to do page->encl->mm->pagetable.  You
could very easily have a VMA analog in there instead of jumping straight
to the mm.